The present invention relates generally to gating grids and methods for manufacturing grids for gating a stream of charged particles.
Certain types of particle measurement instruments, such as ion mobility spectrometers, make use of a gating device for turning on and off a flowing stream of ions or other charged particles. This is accomplished by disposing a conducting grid within the path of the ions. Alternately energizing or de-energizing the grid then respectively deflects the ions or allows them to flow.
The most common method for implementing such a grid uses an interleaved comb of wires, also referred to as a Bradbury-Nielson gate. Such a gate consists of two electrically isolated sets of equally spaced wires that lie in the same plane and alternate in potential. When a zero potential is applied to the wires relative to the energy of the charged particles, the trajectory of the charged particle beam is not deflected by the gate. To deflect the beam, bias potentials of equal magnitude and opposite polarity are applied to the two sets of wires. This deflection produces two separate beams, each of whose intensity maximum makes a corresponding angle, alpha, with respect to the path of the un-deflected beam and deflects them from their normal trajectory.